Antigen-specific suppression of the human T cell response to myelin basic protein (MBP) represents a potential therapeutic modality for multiple sclerosis (MS). This has been accomplished in experimental allergic encephalomyelitis by vaccination with synthetic peptides corresponding to sequences on particular V-beta T cell receptor (TCR) gene products expressed by rat encephalitogenic T cells. However, the human T cell response to MBP appears to be considerably more diverse than in the animal model, with multiple epitopes, major histocompatibility complex (MHC) restriction elements, and TCR molecules being involved. For a similar therapeutic strategy to be successful in MS, a small number of conserved sequences must be utilized by the expressed TCRs. Theoretically, the chance for success would be optimized if the conserved sequences included sites of TCR binding to the peptide-MHC complex. The proposed studies will determine the residues on the TCR that bind to the MBP-MHC complex. Full length cDNAs corresponding to the TCR alpha and beta genes expressed by human MBP-specific T cell clones will be transfected into mutant T cell lines that lack one or both TCR genes. MBP- reactivity of the transfectants will be assayed by: l) production of IL2- specific message, 2) IL2 secretion measured by bioassay, and 3) CD69 expression. Site-directed mutagenesis studies will determine which residues on the TCR alpha and beta chains are required for recognition of the MBP-MHC complex and if conservative vs. non-conservative substitutions generate different patterns of reactivity. These studies will provide valuable information on the fine specificities involved in T cell recognition of peptide antigens, will allow subsequent evaluation of the 3-dimensional configurations of the TCR molecules at the sites of binding to the MBP-MHC complex, and will determine if therapeutic maneuvers aimed at the antigen (Ag)-MHC binding site on the TCR are feasible in attempts to suppress the immune response to MBP.